Aliens are often reported in groups of three, a triad, and this relationship is even observed during visits from entities in light form. The triad is not a magical formation, it is a practical arrangement. Human affairs on Earth are seldom outside of the influence of procedures and directives, and then only for a brief period of time. Thus, as they will be held accountable for their actions shortly, they follow the procedures. If mother instructs the child not to talk to strangers and not to cross the street, these guidelines cover most situations the child will encounter while out playing in the yard. The soldier in the trenches, the salesman out on the road, the biologist deep in the jungles - all can rely on their procedures to cover most situations. On the rare occasion where procedures don't apply, policy is used as a guide, which is only procedures made general. Mother's instructions are a policy not to engage in conversation with outsiders, so if the neighbor gets too friendly, the child backs away from this conversation too.
Out and about in the Universe, higher entities find themselves in situations that are totally unfamiliar and unexpected. There are no procedures or even general policy that can apply. An example that humans could relate to would be a setting where one's physical body merges with another's - the two becoming physically one. How does one go about their day? Are conferences between the two entities incarnating this joint body occurring at every point, every beat of the heart, or do they divide up the territory? What occurs where a difference of opinion arises? Another situation humans could relate to would be size differences, where an entity is incarnated into something many times larger or smaller than the physical body of another, with the smaller entities finding themselves on occasion inside the larger. What rules apply? Beyond social interactions in strange social settings, strange physical setting are also encountered. Humans are used to terra firma under their feet, but how might they go about their day in a nebula setting, where nothing is firm and all is swirling constantly.
Triads give the venturing entities a means of quickly making decisions during their ventures. The tie is broken. Either all agree or two of the three agree or two of the three disagree with the third. The issue is instantly settled.